1. Field of the Invention
The present invention relates to a method of the measurement of light from an optical cable.
2. Description of the Prior Art
When light is entered into an optical fiber cable, normally the light is entered from an end of the optical fiber cable. However, in case of connecting two optical fibers it is desired to enter light into the optical fibers at an intermediate position of the optical fibers. As shown in FIG. 1, in connecting two optical fibers 2 and 3, the respective ends 2A and 3A of two optical fibers 2 and 3 are coincided each other with respect to their optical axis, thereafter both ends 2A and 3A are melted and connected together. In coinciding the optical axis of the two optical fibers 2 and 3, light of a light source 1 is applied to the optical fiber 2, transferring the light in the optical fiber 2 to the optical fiber 3 through the ends 2A and 3A. Light intensity at the other end of the optical fiber 3 is measured by a light detector 4 and the adjustment of the optical axis of the optical fibers 2 and 3 is made in such a manner that the maximum output of the detector 5 can be obtained. However, the optical fiber is extended in a unit up to several tens kilometers. Thus, in connecting two optical fibers extending such a length, the above method shown in FIG. 1 is apparently inefficient since the light detector 4 is so far away from the light source 1. In order to make the adjustment of the axis of the optical fibers easy, there has been used a local light application method in which the light is applied in the optical fiber at the position near the end 2A of the optical fiber 2. In the conventional local light application method, the optical fiber 2 is bent in a round manner near the end 2A and the light is applied to the bent portion 2B from a light source 5 through an optical fiber 6 and a lump of matching oil 7 coated on the optical fiber 2.
In the arrangement of FIG. 2, light transmission efficiency varies at the end 6A of the optical fiber 6, the matching oil 7 and the bent portion 2B of the optical fiber 2, whereby the adjustment of the axis of the optical fibers 2 and 3 is troublesome. Also the work of coating the matching oil on the optical fiber 2 is necessary. In addition the optical fiber 2 is stained by the matching oil 7. Moreover, change of the light transmission efficiency decreases the efficiency of the light detection at the light detector 4.